The present invention relates to a holding device for studs which have a radially projecting flange section, comprising a collet component which has a clamping section and a hollow insertion section, it being possible for a stud to be inserted via the insertion section to the clamping section, and the clamping section being designed in order to exert a radially inwardly directed clamping force for clamping the stud in place, a securing device, past which a flange section of the stud can be directed, being arranged on the insertion section and being designed with respect to the clamping section in such a way that a flange section which is directed past the securing device is mounted in a secured manner in a securing position between the securing device and the clamping section.
Such a holding device is disclosed by document EP 1 495 828 B1.
The present invention also relates to a joining head for joining studs to workpieces, comprising such a holding device, and also relates to a method of feeding a stud to a joining head.
In the field of joining technology, it is known to join studs to the surface of a workpiece. This includes “stud welding”, in which a stud is welded to the surface of a workpiece. Alternative joining techniques include, for example, the adhesive bonding of a stud to the surface of a workpiece.
Such processes are frequently carried out in an automated manner, for example in the motor vehicle industry, where a multiplicity of such studs are joined to the vehicle sheet in order to provide anchors for fastening means, paneling, etc. The automated joining of studs to workpieces as a rule includes the provision of a joining head on a robot. The joining head is in this case connected to a supply unit which provides, for example, the electric welding current and other control signals. Furthermore, it is preferred to feed the studs to the joining head in an automated manner. As a rule, this is effected by compressed air through feed tubes. For high cycle times, it is appropriate in this case to feed the studs from the rear, as it were, into a holding device of the joining head. The holding device serves to shift the stud into a defined ready position, starting from which a joining process can be initiated.
The diameter of the feed passages is as a rule slightly larger than the diameter of the flange section in order to make it possible to transport the stud therein with an easy motion. In the holding device, too, the inside diameter of the insertion section is as a rule slightly larger than the outside diameter of the flange section. This may result in a stud fed to the holding device coming into an oblique position in the holding direction and first having to be oriented (centered) again with a welding axis before the stud can be transferred into the ready position. In some situations, it may be the case that this centering does not succeed, the result of which is that the fed stud then has to be ejected from the holding device. In the process, the stud falls downward in an uncontrolled manner, either onto the floor or also, for example in automobile construction, into the body. The ejected studs then lie distributed on the floor and are swept up and thrown away. Studs left lying in a body may subsequently lead to disturbing noises during driving.
The holding device which has been disclosed by document EP 1 495 828 B1 has a securing device in the form of a collet element arranged inside a collet cover. The collet element has a plurality of axially extending arms which can be expanded radially relative to one another.